\(\left(3a+9\right)^2-\left(a^2+3a\right)\)
\(=\left[3a+9-\left(a^2+3a\right)\right]\left[3a+9+a^2+3a\right]\)
\(=\left[9-a^2\right]\left[a^2+6a+9\right]\)
\(=\left(3-a\right)\left(a+3\right)\left(a+3\right)^2\)
\(=\left(3-a\right)\left(a+3\right)^3\)
\(\left(9+3a\right)^2-\left(a^2+3a\right)^2=\left(9+3a-a^2-3a\right)\left(9+3a+a^2+3a\right)=\left(9-a^2\right)\left(9+a^2+6a\right)=\left(3-a\right)\left(3+a\right)\left(a+3\right)^2=\left(3-a\right)\left(a+3\right)^3\)
( 9 + 3a )2 - ( a2 + 3a )2
= 32 ( a+3 )2 - a2 ( a+3 )2
= ( 32 - a2 ) ( a + 3 )2
= ( 3 - a )( 3 + a )( a + 3 )2
